This invention relates generally to gas furnaces and, more particularly, to a method and apparatus for draining condensate from a condensing furnace that may operate at temperatures below freezing.
In order to improve the operating efficiency of residential gas furnaces, it has become common practice to add a condensing heat exchange downstream of the primary heat exchange so as to recover the latent heat of condensation that is otherwise lost to the flue gases that are discharged to the atmosphere. Such a system is shown and described in U.S. Pat. No. 5,439,050 assigned to the assignee of the present invention. Such furnaces are normally located in basements, attics, closets or crawl spaces where the temperatures are relatively warm and from which the resulting condensate can be easily drained without any danger of freezing.
As rooftop air conditioners have evolved to include heat pumps and supplemental heat in the form of electrical resistance heaters, gas furnaces have now come to be incorporated as part of the system. Heretofore, the performance efficiency of the air conditioner has been paramount, with little consideration being given to the heating efficiency of the system. However, as year-around operating efficiencies are becoming more important with increased emphasis on lifetime operating costs, consideration is being given to the possibility of adding a condensing heat exchanger to such outdoor furnace systems.
Unlike a residential condensing furnace, when a condensing rooftop unit operates under subfreezing ambient conditions, disposal of the condensate is a problem. This is also true of other systems located where they are exposed to ambient conditions, such as ground based systems. That is, during heating operation, the condensate may commence to freeze at the discharge end of the drain line and slowly work its way up toward the condensing heat exchanger. Further, once the condensing furnace is turned off, any residual condensate that may be trapped somewhere along the condensing heat exchanger or the drain line, can freeze. The frozen condensate may cause restriction or blockage, and may even backfill the unit with condensate the next time the furnace comes on.
It is therefore an object of the present invention to provide an improved condensate drainage system for an outdoor condensing furnace.
This object and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings
In accordance with one aspect of the invention, a condensate drain line is provided to conduct the flow of condensate from the condensing heat exchanger to a location where the temperature is above freezing to thereby ensure that, during heating operation, the condensate can be properly discharged without freezing.
In accordance with another aspect of the invention, the drain line passes through a space in which the temperature during heating operation is designed to be maintained above freezing such that the condensate is not exposed to freezing temperatures during heating operation.
By another aspect of the invention, the drain line passes through a space in which the temperature during heating operation is designed to be maintained substantially above freezing, such that any condensate that may freeze in the drain line during a furnace-off operation, will be caused to thaw when furnace operation is resumed.
In accordance with another aspect of the invention, the drain line is routed through the compartment containing the primary heat exchanger.
By yet another aspect of invention, the drain line passes into the primary heat exchanger compartment and discharges into a drain pan which is in direct contact with the primary heat exchanger such that during your furnace operation, condensate is caused to vaporize from the drain pan.
By still another aspect of the invention, the drain line passes through the flue of the furnace and terminates just short of the termination of the flue.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.